The instant invention relates generally to cooling systems and more particularly to an air-cycle cooling system for an electric motor. Large electric motors, for example alternating current (AC) induction motors, generate tremendous amounts of heat as a result of the electromagnetic fields therein. The internal heat build-up significantly reduces the efficiency of the motor, particularly in high-density power applications. In electric motor applications heat is particularly undesirable due to the increase in electrical resistance through the motor windings associated with an increase in temperature. AC induction motors utilizing vector drives are particularly prone to heat build-up in the rotors thereof. The removal of this heat is required for efficient operation of the motor.
Known in the art motor cooling systems employ a variety of cooling methods including air fans and various liquid coolants, for example water or transmission fluid, circulated through jackets surrounding the motor frame. In these systems, heat builds up in the rotor and stator and radiates to the inner surface of the water jacket surrounding the motor. Water (or other industrial coolant such as liquid nitrogen) is continuously circulated throughout the water jacket surrounding the motor to dissipate heat from the interior surfaces thereof.
Conventional water jacket motor cooling systems can provide sufficient cooling for ordinary large motor applications, but motor efficiency is unimpressive. In high power density applications, a great deal of power that would otherwise translate into shaft horespower is lost due to heat build-up in the motor""s rotor and stator. Vector drive motor control systems have a particular tendency to cause heat build-up in the rotor surfaces, thereby requiring heat to radiate outwardly through the stator thence to the water jacket interior surfaces. This results in a very poor heat transfer path and an inability to provide adequate motor cooling for high power density applications.
Additionally, known-in-the-art liquid cooling systems greatly increase the expense of a given motor application due to the necessity of providing a coolant supply, piping, temperature and pressure regulation, and the various labor and material costs associated therewith. Furthermore, the effects of chronic and excessive heat build-up are deleterious to electric motors. Exotic industrial coolants that prevent excessive heat build-up for very large motor applications can be cost prohibitive.
The aforementioned problems are solved by the cooling system and method of the present invention that provides a directed airflow to the interior of an electric motor to remove undesirable heat therefrom. The instant invention introduces cooling fluid, preferably compressed air through an end plate of an electric motor utilizing a nozzle, or a plurality thereof, disposed radially outwardly of the end turns of a stator.
The instant invention is designed to operate using xe2x80x9cshop airxe2x80x9d, widely available in most industrial settings, as a preferred cooling fluid. The use of compressed air provides a tremendous cost savings by obviating the need for specialized liquid cooling systems in large motor applications. Additionally, the energy used by industrial compressors to supply xe2x80x9cshop airxe2x80x9d, throughout an industrial plant is partially recovered by employing the air as a cooling fluid. The pressurized shop air is forced through a nozzle, or a plurality thereof, thence into the interior of an electric motor thereby creating a rapid pressure drop as the air enters a chamber in the motor. Since the volume of the compressed air exiting the nozzles is essentially constant, the gas law (PV=nRT) requires the air temperature to exhibit a proportional decrease.
The cool air exiting the nozzles is directed tangentially to the axis of the rotor at a plurality of points outwardly of the end turns of the stator. This cool, high velocity fluid travels through the channels formed by the looped electrical conductors inherent in conventional stator end turns, and is thereby directed radially inwardly across a rotor end disc, proximate the rotor shaft, and then into the slight air gap between the rotor and stator, thus efficiently removing heat from the both rotor and stator surfaces. The rotation of the rotor and a slight positive pressure maintained between the upstream and downstream ends of the motor provide for high velocity cooling fluid within the rotor-stator gap.
The cool air then travels inwardly across the end disk of the motor to transfer heat therefrom. The air then exits the motor through a plurality of exhaust ports disposed in a second motor end plate located opposite the drive end thereof. The exhaust ports are preferably sized to maintain a slight positive pressure differential between the chamber at the drive end of the motor and the chamber at the exhaust end thereof, depending upon the pressure of the cooling air supply. This positive pressure differential enhances the flow of cooling fluid through the rotor-stator gap, providing exceptional heat transfer. In one embodiment of the instant invention a plurality of exhaust ducts having inlets located radially outwardly of the stator end turns are disposed in fluid communication with the exhaust ports to direct the cooling fluid exiting the rotor-stator gap across and through the stator end turns, thereby enhancing overall heat transfer.
The instant invention is readily retrofitted to existing electric motor applications, requiring only several apertures to be bored in one end plate for installation of the plurality of nozzles, and an exhaust port or ports in the opposed end plate. In most industrial settings, compressed air to be used as cooling fluid is readily available via plant piping. The motor may be equipped with a water jacket or similar cooling apparatus that remains unused for purposes of the instant invention
Therefore, one object of the instant invention is an inexpensive cooling system for conventional electric motors, of particular benefit in high power density applications.
Another object of the instant invention is a cooling system for an electric motor employing widely available xe2x80x9cshop airxe2x80x9d as a cooling fluid, thereby obviating the need for costly liquid cooling systems.
Another object of the instant invention is a cooling system for an electric motor that recovers a portion of the energy expended in the production of compressed air in industrial facilities.
Another object of the instant invention is a cooling system for an electric motor utilizing a plurality of fluid nozzles to direct cooling fluid to cool the rotor and stator thereof, thereby providing a dramatic increase in motor efficiency.
Another object of the instant invention is a cooling system for an electric motor that permits the operation thereof in extremely high power density applications, wherein conventional cooling systems fail.
Yet another object of the instant invention is a cooling system for an electric motor that utilizes the existing channels present in conventional stator end turns and motor windings as flow paths for cooling fluid, thereby affording exceptional heat transfer.
Yet another object of the instant invention is a cooling system for an electric motor that is readily installed in existing motor applications.
Additional objects, features, and advantages of the present invention will become apparent from the subsequent detailed description, taken in conjunction with the accompanying drawing figures.